1. Technical Field
The present invention relates to a manufacturing management method for a mounter which manufactures mounted boards by mounting components on boards. The present invention also relates to a manufacturing management method for a manufacturing line including plural mounters.
2. Background Art
Conventionally, manufacturing lines have been used when manufacturing mounted boards by mounting electronic components onto boards, such as printed circuit boards. These manufacturing lines are manufacturing lines which manufacture mounted boards on moving assembly line in which apparatuses with respective roles are arranged in line. The assembly line includes: an apparatus for printing solders on boards; an apparatus for applying adhesive to the boards; an apparatus for mounting electronic components onto the boards; and an apparatus for soldering the electronic components to the boards.
In order to obtain a high throughput for the manufacturing line as a whole, a high throughput is also required for each manufacturing apparatus, for example, a mounter which mounts components onto boards. Thus, in order to realize this, for the mounter, hardware measures for transporting components at high speed in each of the following processes are adopted: a pickup process in which each component to be supplied to the mounter is picked up, held, and lifted by vacuum; a transporting process in which the picked-up component is transported from a component supply unit to a point above a board; and a mounting process in which the transported component is placed down and mounted onto the surface of the board. Meanwhile, software measures are adopted for optimizing the arrangement sequence of component feeders and component tapes, and optimizing the arrangement sequence of components (See Patent Reference 1, for example).
Thus, by maintaining a high-throughput manufacturing line like this, mounted boards are manufactured as planned fully in accordance with a manufacturing plan that is drafted based on a sales forecast, which is information from the sales department and so on.
Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2002-50900
However, information such as sales forecasts, which serves as a base for manufacturing planning, is mere predicted values. Meanwhile, a manufacturing plan is drafted for a comparatively long span, for example, by the year or by the month. Thus, it is often the case that a difference occurs between the mounted boards to be manufactured according to daily operation planning based on such manufacturing planning and the mounted boards to be actually shipped (sold).
If any difference occurs like this between the planned value and the result value, a situation arises which necessitates storage of finished mounted boards within a manufacturing factory, that is, carrying an inventory, while inventory runs out which makes it impossible to ship (sell) the mounting boards as a result of manufacturing bottleneck.
Generally, inventory shortage affects downstream processes, for example, even a process in which products are finished by attaching a mounted board. Thus, a manufacturing plan tends to generate excess inventory rather than inventory shortage. Any generation of such inventory necessitates storage space for mounted boards and thus causes storage expenses and so on.
In addition, in order to deal with unstable factors such as an abrupt change in planning despite a margin for delivery time, it is more likely to try to finish manufacturing a predetermined quantity at an earlier date by continuing the manufacturing of mounted boards while keeping a high throughput. In this case, the manufacturing plan is achievable but results in a waste of electric power and an increase in inventory. This leads to an increase in costs including electric expenses.
FIG. 1 is a diagram for illustrating inventory.
For example, assume that, within a factory there are a mounting line 602 which can manufacture 200 boards A per day and a mounting line 604 which can manufacture 150 boards B per day. To this factory, assume that an order 606 of “manufacture 150 boards A and 120 boards B” arrives. In this case, when the two mounting lines 602 and 604 are fully operated to manufacture 200 boards A and 150 boards B, and when the ordered quantity of boards are shipped, the inventory of boards A is 50 (=200−150), while the inventory of boards B is 30 (=150−120). Thus, this leads to cost losses. Note that such inventory of products to be shipped from the factory will be hereinafter referred to as “shipment inventory.”
In addition, in the case where plural mounting lines manufacture a single board or a single product in an interrelated manner and where the plural mounting lines have different takt times with a bad line balance, an inventory is generated in the manufacturing process of boards. Thus, this case also presents a problem which leads to cost losses resulting from carrying an inventory. Note that such inventory generated in the manufacturing process of products will be hereinafter referred to as “process inventory.”
FIG. 2 is a diagram for illustrating a problem related to the process inventory as described above.
For example, assume that there are a board A mounting line 608 for manufacturing boards A and a board B mounting line 610 for manufacturing boards B, and that an assembly process 612 for a board A and a board B follows the two mounting lines 608 and 610. Furthermore, assume that boards A and boards B are manufactured in parallel on the board A mounting line 608 and the board B mounting line 610. In this case, assume that the line takt time (time required for manufacturing a board) for the board A mounting line 608 is 12 seconds, while the line takt time for the board B mounting line 610 is 20 seconds. Thus, when compared in the quantity of boards to be manufactured per unit time, there are more boards A. Consequently, boards A remain as process inventory.
In addition, FIG. 3 is another diagram for illustrating the above problem of process inventory. A manufacturing system 626 shown in the figure is a system for mounting components onto both sides of a board, and includes: a back surface mounting line 622, a stocker 30a, a conveyer 154, a board reversing apparatus 156, and a front surface mounting line 624.
The back surface mounting line 622 is a mounting line which mounts components onto the back surface of each board. The stocker 30a stocks each board the back surface of which is mounted with components. The conveyer 154 transports the board stocked in the stocker 30a. The board reversing apparatus 156 reverses the board transported by the conveyer 154. The front surface mounting line 624 is a mounting line which mounts components onto the front surface of the board reversed by the board reversing apparatus 156. In other words, each board flows in sequence in the direction indicated by the arrows in the figure.
In this regard, assume that the line takt time for the back surface mounting line 622 is 12 seconds, while the line takt time for the front surface mounting line 624 is 20 seconds. Thus, compared in the quantity of boards to be manufactured per unit time, there are more back surface boards. Therefore, the manufacturing of the front surface boards cannot keep up with the manufacturing of the back surface boards, and the back surface boards are to be stocked in the stocker 30a as process inventory.
The present invention, having been conceived in view of problems described above, aims to offer a manufacturing management method for a mounter which suppresses the occurrence of inventory shortage or excess inventory as much as possible, and further to offer a manufacturing management method for enabling power savings in the case where the line is not utilized to its full capacity.